8,928 research outputs found
Prediction of Darcy-Forchheimer drag for micro-porous structures of complex geometry using the lattice Boltzmann method
No full textThe micro flows through two-dimensional and three-dimensional granular and fibrous porous media at various Knudsen numbers are studied by using the lattice Boltzmann method. For the granular materials, the results for the medium of rounded inclusions agree well with the existing empirical and numerical correlations between the permeability and the Reynolds number. However, the agreement becomes poor for the medium of sharp-cornered inclusions. A new correlation for the Darcy-Forchheimer drag for various inclusion shapes and arrangements is then proposed. For the fibrous materials, the current results are also compared with existing experimental and numerical data. They are in good agreement. The calculations are further carried out for these porous media in the slip-flow regime. The effect of rarefaction on the permeability in different porous media is discussed. A new correlation between the permeability, the porosity and the Knudsen number for both granular and fibrous porous media is presented
Lattice Boltzmann study of three-dimensional gas microchannel flows
No full textThe compressibility and rarefaction of three-dimensional (3D) pressure-driven gas microchannel flow is studied by the lattice Boltzmann equation method. The method employs a modified particle distribution function and a Knudsen-number-relaxation-time relation without use of any ad hoc treatment at the wall for the slip velocity. The effects of the aspect ratio of the channel width to height, Ar, and the outlet Knudsen number, Kn(0), on pressure nonlinearity, slip velocity and mass flow rate are investigated. As Ar increases, the slip velocity decreases. As a consequence, the nonlinearity of pressure increases. Their distributions, as expected, get closer to some two-dimensional (2D) limit lines. With Ar being greater than 1, one of the most interesting phenomena is the variation of the slip velocity along the wall due to variation in shear rate. As Kno decreases, the differences between slip velocities Us-z at the bottom and top walls and Us-y at the side walls decrease. The mass flow rate is also calculated and compared with 2D analytical solution. The results show that the mass flow rate through the gas microchannel decreases with decreasing Ar. On the other hand, as Ar increases, the computed mass flow rate gets closer to 2D analytical solution
DFT calculation on the thermodynamic properties of polychlorinated dibenzo-p-dioxins: Intramolecular Cl-Cl repulsion effects and their thermochemical implications
No full textPolychlorinated dibenzo-p-dioxins (PCDDs) are one of the most intensively studied chemical pollutants. However, the absence of reliable thermodynamic data on PCDDs seriously limits quantitative understanding of their formation and distribution at combustion sources. By carrying out a DFT calculation (B3LYP/6-31G**) for thermodynamic properties of 75 PCDD congeners, we find that previous thermodynamic estimations on the gas-phase enthalpies of formation (DeltaH(f)) and Gibbs free energy of PCDDs were seriously misestimated, particularly for highly chlorinated congeners, largely as a result of underestimating the intramolecular Cl-Cl repulsion energy. The disagreement between the DFT calculation and other methods becomes progressively larger with increasing chlorine substitution. Octachlorodibenzo-p-dioxin (OCDD) that has been considered as the most thermodynamically stable congener in previous calculations turns out to be much less stable. The differences in calculated DeltaH(f) values between OCDD and the most toxic congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin, or other laterally chlorinated (2,3,7,8-substituted) toxic congeners are within 1 kcal/mol. Most DeltaH(f) values for congeners with five to eight chlorines differ by only 1-2 kcal/mol, since the decreasing electronic energies with increasing the number of chlorines in PCDDs are counterbalanced by increasing Cl-Cl repulsion energy. The intramolecular chlorine repulsion effects in PCDDs are systematically analyzed by using isodesmic reactions.X115862sciescopu
Calculation of Accumalated Energy Ratio in Paraffin Waste Form of Radioactive Liquid Concerntrate Considering Various Packing Configuration
No full textMetallorganic chemical vapor deposition of metallic Ru thin films on biaxially textured Ni substrates using a Ru(EtCp)2 precursor
No full textRuthenium (Ru) films on rolling-assisted biaxially textured Ni substrates (RABiTs) were deposited by liquid source chemical vapor deposition using bis-(ethyl-π-cyclopentadienyl)ruthenium (Ru(C2H5C 5H4)2). The thermal decomposition process of the precursor was investigated by Fourier transform infrared spectroscopy (FTIR), mass spectroscopy, and differential scanning calorimetry/ thermogravimetric analyses (DSC/TGA). The crystalline structure and resistivity of Ru thin films were investigated. The Ru films were polycrystalline and had a grainy structure. Although the thermal decomposition of the precursor required a sufficient amount of oxygen, the experimental results showed that up to a certain concentration of oxygen (i.e. O2/Ar ∼ 30/10), Ru metal film was deposited without any detectable RuO2 impurities. A higher deposition temperature and a higher ratio of O2/Ar will be beneficial to the growth of (0 0 2) orientation. They showed a low resistivity of about 10-20 μΩ cm, which is sufficiently low for them to be used as a buffer layer in superconductor tapes or electrode materials in dielectric capacitors.Department of Applied Physic
Unimolecular dissociation dynamics of vinyl chloride on the ground potential energy surface: The method of excitation and product state distributions of HCl and Cl fragments
No full textThe unimolecular dissociation dynamics of vinyl chloride on the ground electronic potential energy surface have been investigated. The vibrationally excited vinyl chloride in its ground electronic state is prepared using the isomerization process of alpha -chloroethylidene radical to vinyl chloride via the: hydrogen atom migration, where the chloroethylidene radical is produced by the ultraviolet photolysis of 3-methyl-3-chlorodiazirine. The vinyl chloride molecule formed in this excitation scheme is highly vibrationally excited in its ground electronic state due to the bond formation between two carbon atoms, and undergoes unimolecular reactions of HCl elimination or C-Cl bond fission. The rotational and vibrational state distributions of the HCl fragments and the spin-orbit state branching ratio of the Cl atoms have been measured with a resonantly enhanced multiphoton ionization (REMPI)/time-of-flight mass spectrometry. The overall state distributions of the HCl and Cl fragments are much colder than those in the 193 nm photodissociation. The rotational distributions of the HCl(nu = 0) and HCl(nu = 1) fragments Fit to the Boltzmann distributions at T-rot = 470 and 130 K, respectively. The vibrational branching ratio of HCl(nu = 1)/HCl(nu = 0) and the spin--orbit state branching ratio of Cl*(P-2(1/2))/Cl(2P(3/2)) are measured to be 0.15 +/- 0.03 and 0.15 +/- 0.02, respectively. The differences in the dynamical observations of vinychloride produced by this excitation scheme and the 193 nm photoexcitation are interpreted in terms of the large difference of excitation energies between two excitation schemes.This work was supported by the Korean
Science and Engineering Foundation (Project No. 0199041-1-1).
Brain Korea 21 Project
Open access self-archiving: An author study
No full textThis, our second author international, cross-disciplinary study on open access had 1296 respondents. Its focus was on self-archiving. Almost half (49%) of the respondent population have self-archived at least one article during the last three years. Use of institutional repositories for this purpose has doubled and usage has increased by almost 60% for subject-based repositories. Self-archiving activity is greatest amongst those who publish the largest number of papers. There is still a substantial proportion of authors unaware of the possibility of providing open access to their work by self-archiving. Of the authors who have not yet self-archived any articles, 71% remain unaware of the option. With 49% of the author population having self-archived in some way, this means that 36% of the total author population (71% of the remaining 51%), has not yet been appraised of this way of providing open access. Authors have frequently expressed reluctance to self-archive because of the perceived time required and possible technical difficulties in carrying out this activity, yet findings here show that only 20% of authors found some degree of difficulty with the first act of depositing an article in a repository, and that this dropped to 9% for subsequent deposits. Another author worry is about infringing agreed copyright agreements with publishers, yet only 10% of authors currently know of the SHERPA/RoMEO list of publisher permissions policies with respect to self-archiving, where clear guidance as to what a publisher permits is provided. Where it is not known if permission is required, however, authors are not seeking it and are self-archiving without it. Communicating their results to peers remains the primary reason for scholars publishing their work; in other words,
researchers publish to have an impact on their field. The vast majority of authors (81%) would willingly comply with a mandate from their employer or research funder to deposit copies of their articles in an institutional or subject-based repository. A further 13% would comply reluctantly; 5% would not comply with such a mandate
Schematic structures for ILs such as TEAP, TEAS, [Bmim][Cl] and [Mim][Cl].
No full text<p>Schematic structures for ILs such as TEAP, TEAS, [Bmim][Cl] and [Mim][Cl].</p
On the nature of the dependency between a numeral and a classifier. Linguistic Research 28.3
No full textChoi, Kiyong. 2011. On the Nature of the Dependency between a Numeral and a Classifier. Linguistic Research 28(3), 517-542. In this article, I claim that a numeral and a classifier each instantiates distinct heads and that the former has a classifier phrase as its complement in numeral classifier constructions in Korean. I also claim that in Korean, a head-final language, the surface word order between a numeral and a classifier, which is Num-Cl, is obtained via head movement of Cl to Num. When Cl is a genuine classifier, the movement is obligatory due to its clitic-like property, while when Cl is an ordinary noun with [+numerable], it is optional. (Kwangwoon University) 1
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